Overload switch for alternating current



Juqe 1o 1924 IL- SCHGN ET AL ovsnnom swirca FOR wrznunma cumin Original Filed Sep t. 4. 1920 V Patented June 10, 1924.

UNITED STATES PATENT OFFICE.

LUDWIG SCII6N AND JAKOB PFRETZSCHNER, OF ESSEN, GERMANY, ASSIGNORS TO FRIED. KRUPP AKTIENGESELLSCHAFT, OF ESSEN-ON-THE-RUHR, GERMANY.

OVERLOAD SWITCH FO'R ALTER-NATING CURRENT.

Original application filed September 4, 1920, Serial No. 408,383. Divided and this-application filed September 3, 1921.

Serial No. 498,442.

(GRANTED UNDER THE PROVISIONS OF THE ACT OF MARCH 3, 1921, 41 STAT L., 1313.)

T 0 all whom it may concern:

Be itknown that we, LUDWIG SorroN, residing at Essen, Germany, and JAKOB PFRETZSCHNER, residing at Essen, Germany, both subjects of the Republic of Germany, have invented a certain new and useful im-, provement in Overload Switches for Alternating Current, of which the following is a specification.

This is a division of our patent application Ser. No. 408,383.

This invention relates to overload switches foralternating current having a magnetic field adapted to be excited both by the current of the circuit which is to be protected and by an auxiliary circuit. The object of the invention is first and foremost to provide an overload switch of the type above referred to which possesses the property of notbeing able to close spontaneously again after the removal of the disturbing cause but on the contrary remains open until the auxiliary circuit .is interruped anywhere. In the second place it is the object of the invention to give the overload switch such a form that it constitutes also an automatic device for connecting in parallel two alterating current circuits. This double object is attained by providing a small motor cooperating with a transformer, to which motor the movable part of the switch is positively connected. Such overload switch, the construction ofwhich is moreover the like for both employments, is distinguished by simplicity convenience of manipulation and great reliability of action.

The invention will be described with reference to the accompanying drawings which illustrate diagrammatically two embodiments of an overload switch according to the said invention.

Figure 1 shows a device suitable for the use in single phase circuits and Figure 2 a similar device suitable for the use in three phase circuits.

In the overload switch illustrated in Figure 1 there is mounted upon the shaft of the rotor Gr of a single phase motor of the repulsion type an arm 9 which terminates in a pin g3 By the aid of this pin it engages in a slot k in a bar If pivoted to the contact brush H of the switch placed in thecircuit which is to be interrupted. In

this circuit which may be intended to supply a current consumer, is included also a bipolar hand-operated switch J and the primary winding K of a transformer. The secondary circuit of the transformer, which contains its secondary winding K and the field winding G of the motor connected in series, is connected to the main current circuit in parallel with the interruption point thereof.

When the switches H and J are closed and the current consumer is taking current normally, the branch circuit containing the field winding G of the repulsion motor is only traversed by the weak current which is induced in the secondary winding K of the transformer K K The strength of this induced current, which is proportional to the strength of the current flowing in the primary winding K, does not suflice however to produce in the motor G, G a. turning moment which would be suflicient to open the switch H. The conditions are preferably so arranged that only in the case of an absolutely fixed current strength in the main current circuit exceeding the normal does the tractive force of the switch motor overcome the spring power of the switch, and move the switch H. into the switched out position shown. After such interruption in the main current circuit a current flows from the main across the windings K, K and G now in series, which current is strong enough to impart to the motor a turning moment by which the switch H is held fast in the switched out position. Only when the current consumer, which had caused the excessive rise of the current strength in the main current circuit, has been switched off by opening the hand operated switch J is the current out off from the shunt containing the windings K and G whereby the motor G, G loses its turning moment and the switch H moves into its switched in position.

In Figure 2 is shown an arrangement suitable for three phase currents. In ac- The arrangementsinFigures 1 and cordance with the number of phases the transformer K, K connected to a three hase main P and the motor switch motor G (supposed in the present case to be an induction motor with a short circuited armature) is three phase and the automatic switch H and the hand-operated switch J, are constructed of tripolar form. M denotes a synchronous machine excited by a nt nuo s u ren whi h, s. d pted t a both as a rotary current generator and a synchronous current motor. The stroke of the automatic switch H is adjustable, in a manner not shown, to a magnitude at which small switch ..movements,' out on the switched; out position of the switch are possible, butwhi'ch does notbring about a closinglof the v inain current circuit;

.Th'e orking of this form of the automatic switch which. acts as heretofore stated when there is an overload, corresponds in all points to that of-the single phase arrangement' shown in' Figure 1. x i

y A 2 posses's however the very important subsidiary action that they can also be used for connecting automatically in parallel, two single or.- pclyphase alternating current circuits.

- This will be more fully explained with reference to Figure 2; Let one circuit be constituted by the main P and the other, which is the oheto be switiched'on, by-the synchronous machine M. So long; as thedirection of rotation of thesynchronous machine M,

forexa'mple, is in the wrong direction or there is: a considerable divergence between its tension, frequency and phase and the corresponding magnitudes of the main P, the field winding (i of the switch motor G, G remains (under the assumption thatthe liand operated switch J is closed) per inanen'tly excited and the switch H remains in the swit hed out position. F

hen the synchronous machine M r0 tates in thecorrect direction, the differences in the tension, frequency and phase, can however be gradually diminished to such an extent that the turningnioment of the inctor switch G, becomes less and less, forthe reason that the excitation of the switch mct'o'i' becomes weaker the snialler the differences mentioned above become. In consequence thereof the H begins to execute ifio'y'ement s which gradually be'coiii'e larger but still do not sufli'ce to bring it into the switched in position.

As soon as thecondition of the approxi 'coiicoidance ,of tension, frequency aiid phase, which as i's wellknown is periodically repeated, lasts long enough, the turning moment of the switch motor G, G drops to such an extent that the spring powei' of the switch preponderates', whereup'cn' the switch at once switches in. The

main P and the synchronous machine M are then connected up in parallel. The switch motor G, G isnow no longer excited by the main tension but by the tension induced in the transformer K, K In the case of overloads the switch works therefore in exactly the same, way as the switch motor shown in Figure 1. \Vhen a switching out has taken place owing to overloading, the parallelconnection is of course also cut-out in consequence thereof. As soon as the cause which produced the overload has ceased to act, the parallel connection will be restored in the manner described above.

Claims. 1 V H V 1. In an electricalprotective: system a main circuit, an overload switch insaidcin cuit, means normally tendingnto close said switch, an auxiliary circuit normally having a current therein responsive to the cur: rent in the main circuit, an electric. motor excited from said. auxiliary circuit. and operatively connected to saidswitchcfor opening the same against said closing means and for retaining said switch in the open position and means for interrupting the auxiliary circuit to cause said switch to close H 2. In an electrical protective system,..a main circuit, an overload switch in said cir, cuit, means normallytending to close said switch, a transformer comprising a: priinary winding in said maincirCuit'v and a secondary winding, one extreniity of which is connected to said primary winding, an auxiliary circuit connectedin-parallel to the break of said overload switch and contain ingsaid secondary winding, motor Opera};

tively connected to said overload switch andcomprising a st-ator winding excited said, auxiliary circuit, and a closed rotoi winding, for opening the said overload switch'and retaining the same open, and a manually operatedswitch in said main' cire cuit for interrupting the current in said auxiliary circuit; I V

r 3; An overload switch for protecting'an alternating current circuit comprising means tending to close the switch, amain' circuit whose current is controlled by the operation of the switch, an auxiliary circuit whose current is permitted to flow indef pendent of said switch control, an electric motor opcratively connected to said switch and dependent upon the simultanedus flew of excessive main and of the auxiliary current, for opening said switch against said closing means, but adapted to retainthe switch in open position by the auxiliarycurrent alone then flowing, means for cutting oif the auxiliary current su'pply to permit the closing of said overload switch, a sepo'nd main circuit cont ining a separate altsinnit: mg current source of approximately the same voltage, frequency, and phase as said first mentioned main circuit, for the purpose of being connected in parallel automatically to said first mentioned main circuit When the overload switch closes; and

conductors connecting said second main circuit to sald overload switch, sald conductors including said means for cutting off the auxiliary circuit supply.

The foregoing specification signed at Es- 10 sen, Germany, this 10th day of August 1921.

LUDWIG soHoN, JAKOB PFRETZSCHNER. 

